Polyalkylene oxides, represented by polyethylene oxide, are known to have a wide range of applications, for example, in fire-extinguishing agents, dispersants, thickener of fabric, antistatic agents, and flocculants. Polyalkylene oxides are thus industrially useful water-soluble polymers. For example, when being added to an aqueous medium, a polyalkylene oxide increases the viscosity of the aqueous medium. This thickening effect caused by the polyalkylene oxide can reduce the frictional drag of the aqueous medium inside a pipe in the process of delivering the aqueous medium through the pipe, enabling efficient delivery of the aqueous medium (e.g., see PTL 1). In particular, polyethylene oxide added to fire-extinguishing water reduces the frictional drag between the water and the pipe when the water flows through the pipe. This increases the velocity and flying distance of fire-extinguishing water sprayed from the pipe, thus enabling efficient fire extinction (e.g., see PTL 2 and 3). In addition, the thickening effect of the polyalkylene oxides can enhance the adhesion of fire-extinguishing water to the target of the fire extinction and delay the evaporation of the water, enabling more effective fire extinction.